What about using exhaust to heat svo?

For discussing the modifications needed for diesel vehicles to run with 2 tank veggie oil conversions.

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What about using exhaust to heat svo?

Postby Luckyr » Sat Dec 04, 2010 11:10 pm

My buddy and I were brainstorming of cheap ways to heat svo and we came up with the idea of wrapping some copper tubing around your exhaust or simply running it along the exhaust pipe before it gets to your IP or filter or wherever. My only reservations is that it might get it too hot. But I am no expert, which is why I am asking you all. Any ideas?
1994 Dodge 3500, flatbed, 5.9 cummins, flatbed, dually, 5spd, all around farm truck
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Re: What about using exhaust to heat svo?

Postby coachgeo » Mon Dec 06, 2010 12:55 am

Luckyr wrote:... Any ideas?
best idea for ya is "if you have not done so.... search around before you ask"

keywords exhaust wrap* WVO* oil would be a good starting point I'm guessing. Not much actually on this board on this topic mostly cause this board was spawned by folk rather educated in advance from other boards, but were tired of ego's and pimping.

Others will chime in aswell. We do need to re-explore this topic on this board IMHO rather it be for sake of newbee's like yourself who venture here or just to see if a new idea gets sparked that changes some thinking on the topic.

Present thinking.... won't work.... exhaust temp ranges varry too much, get too hot, gets heat to oil to slowly in time between start up and good temps compared to using coolant.
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Postby mike_belben » Wed Dec 15, 2010 2:25 pm

there is no chance it will get too hot. it wont get very hot at all is the problem. air insulates too well and you wont be able to wrap thick copper tight enough to actually touch. i have made a few versions of waterheater pre-heat devices off my woodstove.. 4 wraps of 1/2 copper around my 500* F smokepipe didnt transfer heat fast enough to warm flowing water appreciably. yes, it will raise the temp of anything in the lines when standing.. but that amounts to a soda can of hot stuff in 20 minutes.

i ended up submerging the coil in a pot of water ontop the stove, and it works phenomenal, and includes a 212*F fuse, the water.

the only way i believe you can get exhaust to heat veggie is to make a box that the exhaust pipe passes directly through, the more surface area the better. fins coming off the tube, or divide down to several smaller pipes, etc. but its gonna have to be stainless if you dont wanna deal with poly.
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Postby coachgeo » Wed Dec 15, 2010 11:00 pm

mike_belben wrote:there is no chance it will get too hot. it wont get very hot at all is the problem. ...
exhaust pipe temps vary widely when driving and in distance from the manifold. Too hot has been mentioned when using manifold heat not exhaust pipe heat if I recall correctly. In my old Motorhome the manifold/headers would glow red hot. I think that would be a bit too hot.

Though brazing directly to an exhaust pipe as you wrap it to ensure full contact and reduce vibration issues might get to hot too? particularly if near manifold. If you try it.... you MUST have flex line connecting to hard line on exhaust to accomidate for movement.
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Postby mike_belben » Thu Dec 16, 2010 12:28 am

glowing red is a WOT + turned up injection pump kind of thing. my 650ft/lb dodge runs down the road at 400-600 at the manifold, 800 is WOT, empty truck.

not many vehicles these days are leaving that kind of space, where you could get something so close to the manifolds, and beside that, you wouldnt want whatever metal you use to go through that aggressive of a heat cycling regimen.

space constraints will probably require locating further back and taking advantage of the more constant 200-400 degree exhaust temps.

if you are real handy with the welder and machinery, and love complexity, its possible to fab a double wall section of exhaust pipe where the space between walls is filled with coolant, circulated by a 12v pump to a heat exchanger within a dewatering vessel.. vaccuum will drastically reduce the temps and time required. a closed system like that will require some form of safety valve to prevent explosion, similar to a water heater t&p relief. i would not waste my time fabbing the exhaust section out of anything but stainless, and you better be sure the connections are good or itll be batches of anti-freeze veggie.
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Postby David » Sat Dec 18, 2010 3:25 am

Like a lot of things in the veg world, this seems to be another topic subject to more flawed " Mental Arithmetic" conclusions than factualy tested ones and the general consensus on the subject certainly reflects that.

I gave this a shot earlier in the year and found that most of the parroted reasons why it won't work are completely off base.
My conclusion is that it would most certainly work but the effort required makes it a lot easier, simpler and more reliable to use the traditional coolant system.

I found the touted mantra of the oil getting too hot was the complete opposite in reality as Mike suggests.

I clamped over a metre of copper pipe to the headers just as soon as they exited the manifold with 6 muffler clamps and could not get enough heat into the oil to do anything more that make it lukewarm.
On my truck, I can start the thing up and let it idle for 20 min and still put my hand on the header pipes . Sure the temps go way up whent the thing is working but so does the fuel flow rate so one cancels out the other to a point.

The trick to making this work is surface area and having 2 round shapes clamped together gives very minimal contact for any heat transfer.
Yes, you could braze it to the exhaust or you could make a doube wall chamber. I think a good amount of tuning could be achieved by the length of the pipe that was brazed to the exhaust pipe.

I also don't think the temps would vary anywhere near the amount people quote in exhaust temp, particularly if the pipes were joined further back along the exhaust. The exhaust pipe itself has decent thermal mass and also is exposed to a lot of cooling air. While I didn't bother to measure it, I would suggest the temp of the pipe itself would notmally run a far tighter temp range than most people would think because of this.

Also is the fact the oil flowing through the pipe would keep the contact area cooler and stabilise it against any rapid fluctuations.
The change in temps of the oil would be fairly gradual and smooth. Extremes of running such as Idling and full load would probably still be outside the desirable range of the oil temp however.

The problem I saw with exhaust heat is firstly getting enough contact to heat the oil sufficently and then working out what sort of length is requied to get it to heat under normal operating conditions.

My thoughts are with exhaust heat as the primary heat source is that by the time you do set it up, you may as well just go the coolant route and have the benifit of better heat range stability.

Where I do see a benifit of exhaust heat is to partially warm the oil by means of a limited contact patch with the exhaust pipe would be in heating the oil at the rear of the vehicle, IE, close to the point of origin in the tank to make it thinner for its travel along the fuel line to the engine. This may in some circumstances eliminate the need for a larger/ secondary fuel line or booster pump.
It could also be useful for heating the return fuel to the tank to melts fats or just help thin it out from there.

In the end, it was no more difficult for me just to braze up a mother of a coolant powered HE and fit that than what it would have been to use exhaust heat.
No doubt exhaust heat could/would work if you were looking to do something different and enjoy tinkering . If however a person is looking for the simplest and quickest way to heat their oil, then my opinion is that the traditional Coolant powered HE is the way to go.

The big thing with exhaust heat is not too much heat at all, it's getting enough heat into the oil and the regulation of that heat.
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Postby mike_belben » Sat Dec 18, 2010 11:26 am

i am using a smokestack to assist my Sunwizard style heated pickup tube in warming the vegoil tank located right next to the stack. took some IR temps readings last night on the side of the road after pulling up a hill, empty truck.

ambient temp of 16F
engine coolant 170F
EGT (inside manifold) at idle 300F
turbine housing surface at idle 230F
single smoke stack behind cab 135F
veggie tank opposite end from stack 20F
VO inside tank opposite stack 28F
tank surface next to stack 50F
input side of AL heated coolant tube 90F
roof of tank just above pickup/heater loop, near stack 60F

this is my setup
Image

Image

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im convinced it wont be that hard, especially in a van or pickup truck where you could mount a tank down below the frame and plumb exhaust straight through it. but youd always have a hot tank. i expect the average tailpipe exhaust is pretty steadily 200-300F on a full length pickup, near the rear axle. i would spend some money on food grade coating for the inside of the tank, and make the lid something that bolts on with a gasket, rather than welding shut for service, and to prevent burning off the coating when welding. constant heat, bare metal and constant air will make it a poly nightmare.
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